Effects of grazing on ecosystem structure and function of alpine grasslands in Qinghai–Tibetan Plateau: a synthesis

Abstract

1656Abstract. Humans have grazed on the Qinghai-Tibetan Plateau (QTP) for many thousands of years. In recent decades, the intensity of grazing has increased and several new management strategies have been put into place to address the resulting changes in rangeland condition. Effective management of grazing activities in this region requires understanding the impact of livestock grazing across the diverse array of alpine grassland ecosystems present in the QTP, but recent studies have identified a number of critical uncertainties in the ecological science that underlies these management principles. To address these uncertainties, we carried out a synthesis analysis of the effect of livestock grazing on 26 indicators of ecosystem structure and function based on 61 studies from 88 independent research sites within the QTP. Our synthesis results indicate that livestock grazing exerts complex controls on ecosystem structure and function, which vary according to local landscape characteristics. We found that grazing contributes to greater plant species diversity (Shannon-Wiener index, Simpson dominance index, and Pielou evenness index significantly increased 0.18, 0.05, and 0.03, respectively, due to grazing), but decreased aboveground biomass (47.15%), soil organic carbon (12.41%), soil total nitrogen (12.75%), and microbial biomass carbon (9.42%). Further, ecosystem function is controlled by interactions between grazing and other landscape characteristics such as elevation and mean annual temperature. The management regime currently in place in the QTP, which involves complete exclusion of grazing in some areas, can have variable effects on grassland health. Therefore, the complexity of these responses is an indication that livestock and grassland management may benefit from a more nuanced management regime than is currently utilized in the QTP.

Impact of grassland contract policy on soil organic carbon losses from alpine grassland on the Qinghai–Tibetan Plateau

“…() found that soil C loss is primarily attributed to the reduced heavy fraction organic carbon. An increase in soil pH is also expected under conditions of intensified trampling, as it causes topsoil removal and lowers the soil surface towards the more alkaline subsoil (Evans et al ., ). With continuous (nonrotational) grazing under the SMP, plants can be smaller, resulting in less plant cover and biomass, as confirmed in Maqu by our previous studies (Cao et al ., , ), which in turn leads to less C inputs to form SOC (Wang et al ., ; Lu et al ., ). One possible reason for this is that an important portion of the photosynthetic tissue is consumed and subsequent respiration of assimilated C by herbivores increases C outputs from the ecosystem and reduces C available for the formation of SOC (Klumpp et al ., ; Piñeiro et al ., ).…”

Vegetation type and grazing intensity jointly shape grazing effects on grassland biodiversity

“…Globally, grazing patterns are rapidly changing. In some regions such as European mountain ranges, the cessation of grazing is typical, while in most lowland regions of Australia, Africa, Asia, South America, and the Mediterranean, overgrazing has become typical (Abu Hammad & Tumeizi, ; Evans et al., ; Lu et al., ; Rowntree, Duma, Kakembo, & Thornes, ; Vetter & Bond, ). In several regions within the vast Palaearctic steppe zone, which stretches from Eastern Europe to Northeast China, overgrazing, alongside land conversion, became the most important driver of declining grassland biodiversity in the last few decades (Wesche et al., ).…”

An evaluation of government‐recommended stocking systems for sustaining pastoral businesses and ecosystems of the Alpine Meadows of the Qinghai‐Tibetan Plateau

“…A study by Lu et al. () of many paired grazed and un‐grazed grassland sites on the QTP suggested plant species richness declined in the absence of stocking whereas soil carbon, nitrogen, and microbial biomass increased.…”

“…It is possible that differences in perceived degradation arose from a combination of factors such as the cooccurrence of drought and grazing rather than stocking rate per se. A study by Lu et al (2017) of many paired grazed and un-grazed grassland sites on the QTP suggested plant species richness declined in the absence of stocking whereas soil carbon, nitrogen, and microbial biomass increased.…”